This research will investigate whether mutualisms can mediate trophic cascades, and specifically whether parasites of bumblebees can affect plant populations, via three approaches. First, theoretical models will be used to explore how the interreliance of mutualists changes the effects of antagonists on mutualist populations. Second, a multi-site survey will be conducted, correlating incidence of bumble bee parasitism with reproduction of five plant species that vary in their dependence on bumble bees for pollination. This design tests the prediction that there will be stronger negative correlations between parasitism and plant reproductive success for plants that are more dependent on bumble bees. Finally, studies of bumble bee behavior using cage experiments will be used to investigate the impacts of parasitism on foraging behavior and pollination efficiency, and to establish whether changes in behavior due to parasitism can affect pollination. Mutualisms, ecological interactions between two species in which both benefit, are becoming recognized as major structuring forces in biological communities. A key concept in community ecology is that of the trophic cascade, in which predators affect plants through effects on herbivores. However, this concept has never been explicitly applied to mutualisms. Predators and parasites have the potential to negatively affect both their prey and their prey's mutualist partners. Furthermore, the potential for trophic cascades through mutualist interactions will likely be influenced by the degree to which partners rely on each other. Broader impacts include training of a Ph.D. candidate and potential application to agriculture. Parasites have had a dramatic effect on populations of managed honeybees, yet we are only beginning to understand how they can impact native pollinators. This research will enable better understanding of antagonists of pollinators, thus helping us preserve their $200 billion value to the world economy.
